On inclusion (Visit I), a thorough explanation will be given to each patient on the aims and course of the study, as well as a full explanation on dosage, mode of administration, safety and efficacy of Viagra. After reading and signing an informed consent, each patient will be asked to fill a questionnaire regarding his sexual function (IIEF-ED Domain). If the patient fits inclusion criteria, he will be referred to the urologist to initiate the study. On the second encounter (Visit II), medical history and physical exam will be performed. The subject will then fill out 3 questionnaires: IIEF (full version), QVS (quality of sexual life questionnaire) and the SEARS questionnaire. Administration of medication will be performed in a double-blinded crossover fashion. Each patient will be provided, at random either 6 tablets of placebo or Viagra 50mg. The patient will be advised to use them on demand. After consuming all 6 tablets, a third visit will be scheduled. On the third visit (Visit III) each patient will be provided with new IIEF (full version), QVS (quality of sexual life questionnaire), the SEARS questionnaire and an EDITS questionnaire. A few other questions on satisfaction will be asked and recorded (questions on the quality of the erection, duration of intercourse, number of sexual acts per night, frequency of intercourse/week, satisfaction from intercourse etc). Each subject will receive another 6 tablets (Viagra/ placebo). Finally, at the last visit (Visit IV) subjects will again fill out the same questionnaires as on visit III. At the end of the study, double-blind codes will be opened and multi-variant analysis of the data will be performed using chi square and annova.